In previous work (PNAS 69: 1540, 1972) it was demonstrated that the Balb/c myeloma protein from MOPC 315 could be made to function as a tumor-specific transplantation antigen. The current work is aimed at determining what role(s) anti-idiotypic antibody, immune lymphoid cells and immune macrophages play in mediating the myeloma specific transplantation resistance. In addition studies to define the immune aspects of threshold resistance in non-immunized mice are being carried out.